1. Field of the Invention
The invention relates to a biocompatible block copolymer, a medical implant which has been produced with the block copolymer, use of the block copolymer for the production of a medical implant, and new .alpha.,.omega.-dihydroxypolyesters for the preparation of the block copolymer. Where the term medicine in used, this is understood as meaning both human and veterinary medicine.
2. Discussion of the Background
The number of biocompatible polymers for medical implants employed in practice is surprisingly small. Apart from the problem of compatibility, this can be attributed on the one hand to the high technical requirements with respect to mechanical strength, sterilizability, biological degradability and the like, and on the other hand to the large number of different administrative regulations in individual countries.
For example, vascular prostheses, i.e. tubular implants having a diameter of about 1 to 6 mm, of nonabsorbable materials such as Dacron, polytetrafluoroethylene and the like are employed for arterial or venous vessel replacements. These vascular prostheses have several adverse effects on their environment. Above all, the adverse change at the anastomosis, i.e. the connecting point with the endogenous vessels, practically cannot be influenced. Regeneration of a functional vascular wall in the region of the known implants is not possible. A covering with functional vascular cells for avoiding a thrombotic occlusion during long-term use occurs, if at all, only under systemic anticoagulation. Known vascular prostheses are consequently foreign bodies, the physical and biological properties of which practically cannot be influenced.
An attempt has been made to influence the biological properties of vascular prostheses by coating with heparin or heparinoids. However, these coatings have only a temporally limited action in qualitative respects.
Polyester diols derived from caprolactone which are employed in the production of biomedical separating devices are known from GB-A 2 067 580.
Block copolyesters and block courethanes which are suitable as plasticizers for PVC are known from U.S. Pat. No. 4,281,077.
J. Polym. Sci. 13(7) 1353-63 (1975) describes block copolyesters with a crystallizine and an amorphous block.
U.S. Pat. No. 3,663,515 describes the preparation of polyesters and polyurethanes based on a polyester diol from caprolactones.
DE-A1 42 24 401 describes a process in which biologically degradable polyesters are cleaved with polyfunctional compounds. The cleavage products are modified by polycondensation.
EP-A1 0 552 896 describes optically active biologically degradable block polymers which are built up only from one chemical type of block unit.
EP-A2 0 295 055 discloses biologically degradable block copolymers which contain only L-lactic acid as the block unit.